A typical gas-turbine rotor arrangement is shown as a partial perspective view in FIG. 1. The rotor arrangement, which is derived from U.S. Pat. No. 6,339,878, issued in the name of United Technologies Corp., comprises a series of rotor blades 2 anchored in a rotor disk 4. The rotor disk is attached to a shaft (not shown), which is rotated by the action of a working fluid on the rotor blades.
A more detailed view of a known type of rotor blade is shown in FIGS. 2(a) and 2(b). The blade is made up of an aerofoil section 10, a platform 12, a shank 14 and a root 16. The root 16 engages with a correspondingly shaped slot in a rotor disk. The root 16 is configured as the well known “fir tree” shape (see also FIG. 1), this being often preferred because of its excellent resistance against the centrifugal forces exerted upon the rotor blade when the disk is rotated at high speed.
In use, the blade is subjected to considerable stresses, due to the very high temperature of the working fluid flowing over the surface of the aerofoil section 10. In order to lengthen the life of the blade, the blade is often cooled by passing a cooling fluid through cooling ducts provided inside the blade. FIG. 2(b) shows two separate such ducts 18 and 20. Duct 18 is defined by the inside walls of the aerofoil section and a first partition 22, which isolates the duct 18 from the rest of the inside of the aerofoil section. Duct 20 is in three portions divided by second and third partitions 24 and 25. Partition 24 does not reach all the way to the top of the aerofoil section 10, but leaves a gap so that cooling fluid can flow from the first duct portion to the second. Similarly, partition 25 extends from the top of the aerofoil section 10, but ends short of the bottom of this section, so that the cooling fluid in the second portion of duct 20 can rise into the third portion of the same duct. In order to supply cooling fluid to the ducts 18 and 20, in the example shown two fluid inlets 26, 28 are provided. Cooling-fluid flow is then from outside the blade through the inlets 26, 28 and into the ducts 18, 20, as shown in FIG. 2(b). The fluid leaves the blade through holes provided in the leading and trailing edges of the aerofoil section, as shown by the arrows 30, 32, respectively (see also FIG. 2(a)). In some blades the cooling fluid may leave from the top of the aerofoil section (at the so-called “shroud”).
In order to supply cooling fluid to the inlet 28 in FIG. 2(b), a duct is provided in the disk, which carries cooling fluid from outside the disk to the slot, from where it flows into the inlet 28. An example of this arrangement is given in FIGS. 3(a) and 3(b). This example is taken from U.S. Pat. No. 4,344,738 to assignee United Technologies Corp. and shows the fir-tree shaped slot 40, the duct 42 in the disk, an outlet 44 at the radially outer end of the duct 42, and an inlet 46 in an end-face of the disk. Also shown is the bottom portion 48 of the slot and the direction of flow 50 of the hot working gases. Cooling fluid passes through a bore section 52 along a flowpath 54 and turns in a radial direction, where it passes along a further flowpath 56 (see arrows 58). The fluid then enters the inlet 46, passes through the duct 42 and leaves at the outlet 44, where it finally enters a cooling passage in the blade 58, similar to that associated with the inlet 28 in FIG. 2(b).
As regards the inlet 26 shown in FIGS. 2(a) and 2(b), this may be supplied with cooling fluid in the manner shown in FIG. 4. FIG. 4 is derived from German Patent Application No. DE 19957225 filed in the name of Rolls Royce Deutschland and shows a partial side view of a rotor disk 60 and rotor blade 62, as mounted in a high-pressure gas turbine engine. The blade is air-cooled by the flow of cooling air 64, which is fed to an inlet 66 in a shank portion of the blade and to an inlet 68 on the underside of the root portion. The inlets 66 and 68 correspond to the inlets 26 and 28, respectively, in FIG. 2(b). Thus, this system is similar to that of FIG. 3, since it supplies cooling air to the blade through the root portion, but complements that with a parallel supply through the shank portion as well.
It should be noted that separate inlets 26 and 28 are not always employed feeding separate cooling ducts 18, 20. Instead either inlet 26 or inlet 28 may be included and these inlets may carry cooling fluid to the whole of the inside of the aerofoil section 10. Also, instead of a single inlet 26 or a single inlet 28, more than one inlet may be employed in either position—for example inlet 28 may be formed as a pair of adjacent inlets and these may supply either separate ducts 18, 20 or a single duct.
It is a problem with these known cooling arrangements that not all the cooling fluid supplied to the disk reaches the cooling duct or ducts in the blades. It is therefore desirable to be able to reduce the cooling-fluid losses, so that the temperature-related stress on the blades can be reduced.